"This new-gen "R-spec" model goes beyond the GT350 Mustang to deliver more of what matters to serious performance enthusiasts, namely less weight, better aerodynamics and a track-tuned suspension.
Ford engineers trimmed the GT350R's curb weight by over 130 pounds compared to a 2016 Shelby GT350 Track Pack model. Nearly half of that loss came in the form of critical unsprung weight due to the use of 19-inch full carbon fiber wheels that are lighter and stiffer than the GT350's standard aluminum-alloy rims. That swap also brings even-stickier Michelin Pilot Sport Cup 2 ultra-performance tires in place of the GT350's Super Sport rubber. The remaining weight drop came from jettisoning the air conditioning, audio system, rear seats, trunk floorboard/ carpet, backup camera and emergency tire sealer/inflator kit as well as the resonators from the exhaust system.
Ironically, Ford will offer an optional Electronics Package for the GT350R that adds back dual-zone air conditioning, 8-inch touch screen with navigation, seven-speaker audio system, turn signal mirrors and more"
Here is your answer op
...removing the rear seat and passenger seat doesn't take but 10 minutes. ...
... A 10 lb difference is wheel weight would make a huge difference on how much power this car puts to the ground.